Semiconductor emitting devices, such as light emitting diodes (LEDs) and laser diodes (LDs), include, but are not limited to, solid state emitting devices composed of group III-V semiconductors. A subset of group III-V semiconductors includes group III-Nitride alloys, which can include binary, ternary and quaternary alloys of indium (In), aluminum (Al), gallium (Ga), and nitrogen (N). Illustrative group III-Nitride based LEDs and LDs can be of the form InyAlxGa1-x-yN, where x and y indicate the molar fraction of a given element, 0≦x, y≦1, and 0≦x+y≦1. Other illustrative group III-Nitride based LEDs and LDs are based on boron (B) nitride (BN) and can be of the form GazInyAlxB1-x-y-zN, where 0≦x, y, z≦1, and 0≦x+y+z≦1.
An LED is typically composed of semiconducting layers. During operation of the LED, a voltage bias applied across doped layers leads to injection of electrons and holes into an active layer where electron-hole recombination leads to light generation. Light is generated in the active layer with uniform angular distribution and escapes the LED die by traversing semiconductor layers in all directions. Each semiconducting layer has a particular combination of molar fractions for the various elements (e.g., given values of x, y, and/or z), which influences the optical properties of the semiconducting layer. In particular, a refractive index and absorption characteristics of a semiconducting layer are sensitive to the molar fractions of the semiconductor alloy forming the layer.
Current state of the art deep ultraviolet LEDs (DUV LEDs) have a low efficiency due to light trapping within the device, light absorption in the semiconductor layers, as well as light absorption in the contact regions. To improve light extraction efficiency for the DUV LEDs, one approach proposes a design using ultraviolet transparent p-type cladding and contact layers, an ultraviolet reflecting ohmic contact, and chip encapsulation having an optimized shape and refractive index.